Exhaust valve

ABSTRACT

An exhaust valve includes: a shaft section; and a head section that is formed in one end of the shaft section and formed with a valve face that seats on a valve seat disposed in a cylinder head of an internal combustion engine, in which the shaft section has a shaft diameter of a constant diameter; the head section has a head diameter that is larger than the shaft diameter; and a thick shaft section that has a diameter smaller than the head diameter and larger than the shaft diameter is formed within a section between a connecting position that connects the shaft section with the head section and a position that is spaced apart from the head front surface opposite to the valve face in an axial direction by a distance that is approximately the same as the head diameter.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2011-009949 filed on Jan. 20, 2011 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust valve of an internal combustion engine, and more particularly to an exhaust valve that can improve mechanical strength.

2. Description of the Related Art

Conventionally, an exhaust valve of such the type is well-known in the related art which includes a valve main part, a valve guide, and a valve stem that has a smaller diameter portion on the side of the valve main part and a larger diameter portion on the side spaced from the valve main part, in which a boundary between the smaller diameter portion and the larger diameter portion is formed in a smoothly curved surface, and a part of the smoothly curved surface is positioned so as to enter into the valve guide at closing of the valve (for example, see Japanese Patent Application Publication No. 2007-16745).

In such the exhaust valve, since a part of the smoothly curved surface of the valve stem is positioned so as to enter into the valve guide at the closing of the valve, sludge such as carbon that is adhered on the side of the smaller diameter portion can be easily scraped off the stem in a curved surface of the boundary between the smaller diameter portion and the larger diameter portion at the closing of the valve.

That is, in the aforementioned exhaust valve, when the sludge is scraped on an inner corner section in a lower edge of the valve guide at the closing of the valve, outward component force in a radial direction of the stem is applied to the sludge, and therefore the sludge is easily scraped off the stem. In the aforementioned exhaust valve, the smoothly curved surface of the valve stem has a function of scraping the sludge in cooperation with the corner section in the lower edge of the valve guide. In addition, because the valve stem has a curved surface and its cross section gradually changes, stress concentration to the valve stem is not produced, and adequate strength is compensated.

However, in the conventional exhaust valve, since a part on the side spaced from the valve main part is formed to be the larger diameter portion and a part on the side of the valve main part is formed to be the smaller diameter portion so that the sludge is scraped on the inner corner section in the lower edge of the valve guide at the closing of the valve, the larger diameter portion is allowed to have the adequate strength, and the weight reduction is not taken into consideration.

On the other hand, the strength of the smaller diameter portion against the stress concentration is adequately compensated with its curved surface shape; however, strength in high temperature is not taken into consideration. As a result, there are problems that due to high temperature exhaust gas which flows through the smaller diameter portion, the smaller diameter portion reaches high temperature, mechanical strength deteriorates, and the strength in high temperature is inadequately compensated. The temperature of the exhaust gas tends to increase with a demand for compliance with standards for the internal combustion engine or performance improvement such as power of the engine, and the temperature of the exhaust valve also increases. Therefore, improvement of the strength in high temperature for the exhaust valve is highly desired.

As an improvement measure of the strength in high temperature for the exhaust valve, for example, expansion of cross-sectional area of the valve stem is contemplated first. That is, the diameter of the entire valve stem is increased so as to improve the strength in high temperature. However, when the cross-sectional area of the valve stem is expanded, weight of the valve stem increases, and kinematical performance of a valve lift mechanism decreases. Thus, usage rotational speed of the valve lift mechanism has to be reduced, and it causes the deterioration of marketability of the product. In addition, the expansion of the cross-sectional area of the valve stem causes the cross-sectional area of an exhaust gas passage around the valve stem to decrease and exhaust gas pressure to increase. Therefore, exhaust gas flow is hindered, and it results in performance degradation of the internal combustion engine or poor fuel efficiency.

It is contemplated next that the strength in high temperature is improved by changing material of the valve stem without change in shape or increase in weight. However, when metals that have high strength in high temperature such as rare metals that include nickel (Ni), chromium (Cr), and molybdenum (Mo) are used for the valve stem, although the strength in high temperature improves, the metals of high material cost are used for a part for which relatively high strength in high temperature is not required, and therefore manufacturing cost may increase.

Next, it is contemplated that addition and change of heat treatment are made to the valve stem so as to improve the strength in high temperature. However, when the addition and the change of the heat treatment are made to the valve stem, a heat treatment process is required to be added or changed in manufacturing processes, and therefore costs for equipment itself or change of equipment may increase. In this case, because the entire valve stem is placed in a furnace to be heat-treated, a part for which relatively high strength in high temperature is not required is subjected to heat treatment, and therefore manufacturing cost may increase. Accordingly, even though any measures to improve the strength in high temperature are taken, there has been a problem that the measures are inadequate.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an exhaust valve that has adequate strength in high temperature without increase of weight or manufacturing cost.

The exhaust valve according to a first aspect of the present invention is related to the exhaust valve that includes a shaft section, and a head section that is formed in one end of the shaft section and formed with a valve face that seats on a valve seat disposed in a cylinder head of an internal combustion engine and a head front surface that defines a combustion chamber of the cylinder head when the valve face seats on the valve seat. In the exhaust valve, the shaft section has a shaft diameter of a constant diameter; the head section has a head diameter that is larger than the shaft diameter; and a thick shaft section that has a diameter smaller than the head diameter and larger than the shaft diameter is formed within a section between a connecting position that connects the shaft section with the head section and a position that is spaced apart from the head front surface in an axial direction by a distance that is approximately the same as the head diameter.

With the above structure, in the exhaust valve according to the aspect, the effect can be obtained such that the adequate strength in high temperature can be secured without weight increase or increase in the manufacturing cost. That is, the exhaust valve according to the present aspect is formed to have a larger shaft diameter of the thick shaft section only that requires the strength in high temperature in a specified section, and therefore problems in the conventional exhaust valve can be solved in which the weight is increased by thickening the diameter of the entire valve stem to improve the strength in high temperature. In addition, because the exhaust valve according to the present aspect is made of a general-purpose inexpensive material, rare metals that have high strength in high temperature are not required as the conventional exhaust valve, the metals of high material cost are not used, and therefore the increase in the manufacturing cost can be prevented. Because the exhaust valve according to the present aspect does not require the addition or the change of the heat treatment to improve the strength in high temperature, the heat treatment process is not required to be added or changed in manufacturing processes as the conventional exhaust valve, and therefore the increase in the costs for equipment itself or change of equipment can be prevented. Because the strength in high temperature can be improved as described above, if the temperature of the exhaust gas that is flown from the combustion chamber increases due to the improvement of fuel efficiency or requirements such as exhaust emission control in the future, the exhaust valve that has high mechanical strength can be obtained without the increase of weight or manufacturing cost. In addition, an effect on mobility of the exhaust valve can be reduced, and good movement characteristics can be obtained.

According to the present invention, an exhaust valve that has adequate strength in high temperature can be provided without increase of weight or manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic diagram of a valve train where the exhaust valve according to an embodiment of the present invention is applied;

FIG. 2 is a side view of the exhaust valve according to the embodiment of the present invention;

FIG. 3A and FIG. 3B are a side view and a graph that show distances from a valve head front surface and temperature distribution of the exhaust valve according to the embodiment of the present invention;

FIG. 4 is a graph that shows a relation between material strength and temperature in the exhaust valve according to the embodiment of the present invention;

FIG. 5A and FIG. 5B are diagrams that illustrate cross-sectional shapes of exhaust valves according to embodiments of the present invention; and

FIG. 6A and FIG. 6B are graphs that show the relation between temperature distribution and factor of safety in the exhaust valves according to the embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments in which the exhaust valve according to the present invention is applied to a valve train of an internal combustion engine are described with reference to the attached drawings.

First, structure of the valve train is described. As shown in FIG. 1, the exhaust valve 31 according to the embodiment of the present invention constitutes a part of the valve train 10 of the internal combustion engine, and the exhaust valve 31 is described through the description of the valve train 10.

The valve train 10 includes a camshaft 11, a cam 12 that is provided on the camshaft 11, a rocker arm 13 that is engaged with the cam 12, a lash adjuster 14 that is engaged with a first end of the rocker arm 13, and a valve lift mechanism 15 that is engaged with a second end of the rocker arm 13. This valve train 10 is mounted in a cylinder head 1 of the internal combustion engine (not shown).

In this valve train 10, the rocker arm 13 rotates to the second end of the rocker arm 13 as a supporting point of the valve lift mechanism 15 through the rotation of the camshaft 11 and the cam 12, and thus the valve lift mechanism 15 operates. In addition, the lash adjuster 14 adjusts clearance such as a gap between the cam 12 and the rocker arm 13 and a gap between the rocker arm 13 and the valve lift mechanism 15.

The camshaft 11 is driven through the rotation of a crankshaft (not shown) of the internal combustion engine which is transferred by a camshaft drive mechanism such as a timing chain, and the cam 12 rotates in synchronization with the rotation of the crankshaft.

The cam 12 includes a base circular section 12 a, a nose section 12 b, and a cam surface 12 c that is formed with outer peripheral surfaces of the base circular section 12 a and the nose section 12 c. The valve train 10 is constructed such that when the base circular section 12 a contacts the rocker arm 13, the valve lift mechanism 15 is in a closing state, and when the nose section 12 b contacts the rocker arm 13, the valve lift mechanism 15 is in an opening state.

The rocker arm 13 includes an arm body 13 a, a mechanism engagement section 13 b that is rotatably engaged with the valve lift mechanism 15, an adjuster engagement section 13 c that is rotatably engaged with the lash adjuster 14, and a roller section 13 d that is arranged between the mechanism engagement section 13 b and the adjuster engagement section 13 c and is engaged with the cam 12.

The lash adjuster 14 includes an adjuster body 21, a plunger 22, a check valve 23, and a plunger spring 24. The lash adjuster 14 is arranged at a supporting point opposite to the supporting point with which the valve lift mechanism 15 is engaged on the rocker arm 13, and the lash adjuster 14 is operated with oil that is supplied from the cylinder head 1 as hydraulic fluid. The plunger 22 in the adjuster body 21 vertically slides by elasticity of the plunger spring 24 or hydraulic pressure, and thus the clearance between the cam 12 and the roller section 13 d of the rocker arm 13 is adjusted so as to be removed.

The valve lift mechanism 15 includes: an exhaust valve 31; a valve guide 32 that is supported by the cylinder head 1 and guides the sliding of the exhaust valve 31; a valve seal 33 that is disposed at an end of the valve guide 32 and seals the valve guide 32; a stem end 34 and a valve cotter 35 that are disposed at an end of the exhaust valve 31; a spring retainer 36 that is secured at the end of the exhaust valve 31 with the valve cotter 35; and a valve spring 37 that is interposed between the spring retainer 36 and the cylinder head 1 so as to push the spring retainer 36 in the direction that is spaced apart from the cylinder head 1.

In the valve lift mechanism 15, the exhaust valve 31 is seated on a valve seat 2 that is provided in the cylinder head 1. FIG. 1 shows a state in which the exhaust valve 31 is seated on the valve seat 2, namely a valve closing state.

As shown in FIG. 2, the exhaust valve 31 is made of general-purpose inexpensive steel such as austenitic stainless steel and includes a shaft section 41, a head section 42, and a thick shaft section 43. The shaft section 41, the thick shaft section 43, and the head section 42 are formed in one unit. The shaft section 41 and the head section 42 are connected at a connecting position 31 a in a smoothly curved shape.

The shaft section 41 has a constant shaft diameter D₁, is installed in the valve guide 32 as shown in FIG. 1, and is guided in the valve guide 32 to slide in an axial direction of the valve guide 32. The shaft section 41 has one end where the head section 42 is disposed and the other end that is opposite to the one end and formed with formed with a recess 41 a where the valve cotter 35 is fitted, and the spring retainer 36 is mounted on the end.

The head section 42 is formed in the other end of the shaft section 41 and has a valve face 42 a, a head front surface 42 b, and a head back surface 42 c. The valve face 42 a has a smooth surface so as to seal a combustion chamber of a cylinder head (not shown) when seated on the valve seat 2. The head front surface 42 b is formed with a head diameter of D₂ and defines the combustion chamber of the cylinder head when the valve face 42 a is seated on the valve seat 2. The head back surface 42 c is formed in a conical shape at the opposite side of the head front surface 42 b in the head section 42, and the diameter of the head back surface 42 c gradually decreases from the valve face 42 a to the shaft section 41. The head back surface 42 c is connected to the shaft section 41 at the connecting position 31 a.

The thick shaft section 43 is formed in the vicinity of the connecting portion between the shaft section 41 and the head section 42 and has a diameter D₃. The profile of the vertical cross section of the thick shaft section 43 is formed in an arbitrarily smooth curve, and the outer peripheral surface of the thick shaft section 43 protrudes from the outer peripheral surface of the shaft section 41 to be formed in a convex shape. The thick shaft section 43 may be formed in the axial direction within a section between the connecting position 31 a and a position that is spaced apart from the head front surface 42 b by the distance L₂ that is approximately the same as the head diameter D₂. If the distance L₂ is greater than the head diameter D₂, the thick shaft section 43 interferes with the valve guide 32, and the sliding of the exhaust valve 31 in the axial direction may be hindered. In addition, if the distance L₂ is too short, the thick shaft section 43 may be arranged in a position out of an appropriate position in relation to the strength in high temperature.

As shown in FIG. 3A, the thick shaft section 43 is positioned in a maximum temperature region where a part of the exhaust valve 31 reaches at the highest temperature through the flow of hot exhaust gas. The maximum temperature region is a part where the hot exhaust gas flown from a passage between the valve face 42 a and the valve seat 2 directly hits along the surface of the valve face 42 a, because a plane angle of the valve face 42 a is approximately 45 degree when the exhaust valve 31 is in the opening state. An outflow path of the exhaust gas is subjected to an effect of the shape of an inner wall surface of the cylinder head 1 that surrounds an exhaust port.

Therefore, in the exhaust valve 31, the following position becomes the maximum temperature region. The maximum temperature region is a position at the distance from the head front surface 42 b which is a sum of one-half of the head diameter D₂ of the head front surface 42 b, namely one-half of a valve diameter, and one-half through one-third of lifting amount of the exhaust valve 31. Due to the flow of the hot exhaust gas, as shown in a graph of FIG. 3B, heat produced in the exhaust valve 31 is relatively low in a part where the distance from the head front surface 42 b is short or long; however, in a middle part between the parts where the distances from the head front surface 42 b are short and long, the temperature becomes high, and thus the part becomes the maximum temperature region.

As shown in FIG. 4, in a case where the exhaust valve 31 according to the embodiment gets hot as compared with the case where the exhaust valve 31 is at a low temperature, allowable stress (MPa) with respect to repeat count which is shown with polygonal lines remarkably decreases as observed in a fatigue test with test pieces of the material. Therefore, when the mechanical strength of the region that is subjected to high temperature is improved, the allowable stress can be increased.

As shown in a schematic diagram of FIG. 5A, an inflection point on the aforementioned arbitrarily smooth curve that has a diameter D₃ is designated as P₁ in the thick shaft section 43. A point at which an inclination line that is orthogonal to the line connecting the inflection point P₁ and a center of curvature (not shown) of the inflection point P₁ and that passes the inflection point P₁ and extends toward an upper side of the shaft section 41 from the inflection point P₁ intersects with an axis CL₁ of the exhaust valve 31, is designated as P₂. Here, the inflection point means a point where curving direction changes in a curve and a point where a positive sign or a negative sign of the curvature changes on the curve.

An angle between the line passing the inflection point P₁ and the axis CL₁ is designated as θ₁, and an angle between an inclination line that passes the inflection point P₁ and extends toward the head section 42 in a lower side from the inflection point P₁ (lower side from the maximum shaft diameter) and the axis CL₁ is designated as θ₂. In addition, the range of application is determined between a position where the angle θ₂ is greater than or equal to the angle θ₁ and a distance L₃ from the head front surface 42 b is one-fourth of the head diameter D₂, and a position where the angle θ₁ is greater than the angle θ₂ and a distance L₂ from the head front surface 42 b is two-thirds of the head diameter D₂.

As shown in a schematic diagram of FIG. 5B, an inflection point on the aforementioned arbitrarily smooth curve that has a diameter D₃ is designated as P₃ in the thick shaft section 43. In addition, a point at which an inclination line that is orthogonal to the line connecting the inflection point P₃ and a center of curvature (not shown) of the inflection point P₃ and that passes the inflection point P₃ and extends toward an upper side of the shaft section 41 from the inflection point P₃ intersects with an axis CL₂ of the exhaust valve 31, is designated as P₄.

An angle between the line passing the inflection point P₃ and the axis CL₂ is designated as θ₃, and an angle between an inclination line that passes the inflection point P₃ and extends toward the head section 42 in a lower side from the inflection point P₃ (lower side from the maximum shaft diameter) and the axis CL₂ is designated as θ₄. In addition, the range of application is determined between a position where the angle θ₄ is greater than or equal to the angle θ₃ and a distance L₃ from the head front surface 42 b is one-fourth of the head diameter D₂, and a position where the angle θ₃ is greater than the angle θ₄ and a distance L₂ from the head front surface 42 b is two-thirds of the head diameter D₂.

In the range of application, a section between the thick shaft section 43 and the head section 42 may be formed to be a part where the shaft diameter becomes the minimum, namely a concave section 44. With the structure described above, the weight of the exhaust valve 31 can be reduced.

In the range of application described above, even if the part where the shaft diameter becomes the minimum or the concave section 44 is positioned in a part of the head back surface 42 c, in the case where the part of the head back surface 42 c has the adequate mechanical strength, the concave section 44 is applicable, and the weight reduction can be achieved. In other words, in the case where there is the adequate mechanical strength, even if the part where the shaft diameter becomes the minimum is formed in the part of the head back surface 42 c, it does not result in harmful effects of so-called cupping in which the temperature of the head section 42 increases during a high-load operation of the internal combustion engine to result in deterioration of the strength, deformation, and deterioration of seating quality.

Next, effects of the exhaust valve 31 of the valve lift mechanism 15 according to the embodiment will be described.

Since the exhaust valve 31 according to the embodiment is constructed as described above, the following effects can be obtained. That is, the exhaust valve 31 according to the embodiment is constructed with the shaft section 41 and the head section 42 that is formed in one end of the shaft section 41 and formed with the valve face 42 a that seats on the valve seat 2 provided in the cylinder head of the internal combustion engine. In addition, the exhaust valve 31 according to the embodiment is characterized in that the shaft section 41 has the shaft diameter D₁ of a constant diameter, the head section 42 has the head diameter D₂ that is larger than the shaft diameter D₁, and the thick shaft section 43 that has a diameter smaller than the head diameter D₂ and larger than the shaft diameter D₁ is formed within the section between the connecting position 31 a that connects the shaft section 41 with the head section 42 and the position that is spaced apart from the head front surface 42 b in the axial direction by the distance L₁ that is approximately the same as the head diameter D₂.

As a result, the effect can be obtained such that the adequate strength in high temperature can be secured without weight increase or increase in the manufacturing cost. That is, since only the thick shaft section 43 that requires the strength in high temperature is formed to have a large shaft diameter, problems in the conventional exhaust valve can be solved in which the weight is increased by thickening the diameter of the entire valve stem to improve the strength in high temperature. In addition, since the exhaust valve 31 according to the embodiment is made of a conventional general-purpose inexpensive material, rare metals that have high strength in high temperature are not required as the conventional exhaust valve, the metals of high material cost are not used, and therefore the increase in the manufacturing cost can be prevented.

Since the exhaust valve 31 according to the embodiment does not require the addition or the change of the heat treatment to improve the strength in high temperature, the heat treatment process is not required to be added or changed in manufacturing processes as the conventional exhaust valve, and therefore the increase in the costs for equipment itself or change of equipment can be prevented.

In addition, an excess thickness of a part that has adequate strength in the conventional head section can be reduced through the formation of the concave section 44, and therefore the weight reduction can be achieved.

As shown in FIG. 6, since the exhaust valve 31 according to the embodiment is formed with the thick shaft diameter at the part which gets the highest temperature in the temperature distribution, the strength in high temperature is improved not only in the case that the exhaust valve 31 has the shape as shown in FIG. 6A but also in the case that the exhaust valve 31 has the shape as shown in FIG. 6B, that is, the concave section 44 is provided, and therefore the strength of the part of the thick shaft section 43 is improved, and the factor of safety is remarkably improved. In addition, since the concave section 44 reduces the excess thickness of the part that has adequate strength, while the weight reduction can be achieved, the deterioration of the mechanical strength cannot be observed, and the factor of safety is maintained.

Since the strength in high temperature can be improved as described above, if the temperature of the exhaust gas that is flown from the combustion chamber increases due to the improvement of fuel efficiency or requirements such as exhaust emission control in the future, the exhaust valve that has high mechanical strength can be obtained without the increase of weight or manufacturing cost. In addition, an effect on mobility of the exhaust valve can be reduced, and good movement characteristics can be obtained.

As described above, the exhaust valve according to the present invention has the effects in which the exhaust valve that has the adequate strength in high temperature can be provided without the increase of weight or manufacturing cost, and the exhaust valve according to the present invention is also useful to overall valves that are widely used in a high temperature environment. 

1. An exhaust valve comprising: a shaft section; and a head section that is formed in one end of the shaft section and formed with a valve face that seats on a valve seat disposed in a cylinder head of an internal combustion engine and a head front surface that defines a combustion chamber of the cylinder head when the valve face seats on the valve seat, wherein the shaft section has a shaft diameter of a constant diameter; the head section has a head diameter that is larger than the shaft diameter; and a thick shaft section that has a diameter smaller than the head diameter and larger than the shaft diameter is formed within a section between a connecting position that connects the shaft section with the head section and a position that is spaced apart from the head front surface in an axial direction by a distance that is approximately the same as the head diameter.
 2. The exhaust valve according to claim 1, wherein a concave section that has a shaft diameter smaller than the diameter of the shaft section is formed between the thick shaft section and the head section. 